The third section of Table 2 lists interesting examples where the genetic correlation is close to zero with small standard error. The low genetic correlation between schizophrenia and rheumatoid arthritis is interesting because schizophrenia has been observed to be protective for rheumatoid arthritis [50], though the epidemiological effect is weak, so it is possible that there is a real genetic correlation, but it is too small for us to detect. The low genetic correlation between schizophrenia and smoking is notable because of the increased tobacco use (both prevalence and number of cigarettes per day) among individuals with schizophrenia [51]. The low genetic correlation between schizophrenia and plasma lipid levels contrasts with a previous report of pleiotropy between schizophrenia and triglycerides [52]. Pleiotropy (unsigned) is different from genetic correlation (signed; see Methods); however, the pleiotropy reported by Andreassen, et al. [52] could be explained by the sensitivity of the method used to the properties of a small number of regions with strong LD, rather than trait biology (Supplementary Figure 5). We estimate near-zero genetic correlation between Alzheimer’s disease and schizophrenia. The
